Please help!!! LH gone from 13 days to 8 in one month!!!!!! What does this mean?

I'm really hoping that someone might be able to shed some light on this...

I always OV around day 16. This month it was day 15. I use FF so see a significant rise in BBT after OVing (for several days) and that coupled with a +ive OPK shows that I definitely OVd.

I am currently having tests on my progesterone levels because I have started spotting (very lightly, mixed in with CM) from around 10DPO. My temp often dips on that day, then goes up again briefly before dropping down gradually towards AF. Last month the dip was 10DPO which is the day the spotting started, then back up (although not as high as the highest post-OV temps) and then dropped down. AF arrived on DPO14 (which is normal).

This month I OVd on CD15 (1 day earlier than normal) and then my temps went up as usual, although comparing to last month the coverline and subsequent post-OV temps were higher.

Yesterday (8DPO) I woke up to find a temp dip (down .3). Normally the spotting starts the night of the temp dip but yesterday it was there as soon as I got up. Obviously I was gutted but was just glad I was getting the Progesterone tests done (had one on Friday and have another one this morning as 7DPO was on Saturday ggrrrrrr).

However last night, I noticed that it wasn't my usual spotting mixed in with CM, but brown blood like the start of AF (which I haven't had since I was on the pill 5 years ago before having DD!). In all honesty I was hopeful that it was implantation... But this morning I have woken up and my temp hasn't gone up again like it has on previous months, it's stayed down (just up .01 on yesterday) and the blood is now red, mixed with brown.

I don't feel right. In the night it felt like lots of pressure very low down and boobs were itchy. Today my boobs really ache and my tummy just feels really heavy. Not like AF normally does, but I guess that's what it is. So I've put 'light' menses for my AF and FF has changed my chart to CD1 .

So what can cause the LP to drop so dramatically from 13 days to 8 days, in just one month? I'm nearly 39 and so worried that this is it for me...

I've had unusually short cycles twice - once while actively ttc and once before we were properly trying but not being very careful. I was tracking my cycles for the one where I was actively ttc and I got AF at 9dpo. I believe, but can't prove it, that in both of these cases, something attempted to implant but failed, and that triggered AF. I saw my acu lady about 12 hours before bleeding started and when I saw her next and told her what had happened she looked back and had written "pregnant?" in her notes for the previous visit.

I was back to normal the next cycle. So my recommendation is to see what happens next month.